Recommended Dosage and Treatment Regimen for Cephalexin (Cefalexin)
For adults, cephalexin should be administered at 500 mg three times daily for most infections, with adjustments based on infection severity and type. 1
Adult Dosing Recommendations
Standard Adult Dosing:
- Typical dosage: 250 mg every 6 hours (1 g daily) to 500 mg every 6 hours (2 g daily) 2
- Alternative regimen: 500 mg every 12 hours for specific infections:
- Streptococcal pharyngitis
- Skin and skin structure infections
- Uncomplicated cystitis in patients over 15 years 2
Dosing by Infection Type:
- Skin and soft tissue infections: 500 mg three times daily 1
- Urinary tract infections: 500 mg three times daily or 500 mg every 12 hours for uncomplicated cystitis 1, 2
- Human bite infections: 500 mg four times daily 1
- Chronic urinary tract infections: 1 g twice daily for 10 days has shown comparable efficacy to four-times-daily dosing 3
Maximum Dosage:
- Maximum daily dose: 4 g
- For severe infections: Larger doses may be needed, but if daily doses greater than 4 g are required, parenteral cephalosporins should be considered 2
Pediatric Dosing Recommendations
Standard Pediatric Dosing:
- Usual recommended daily dosage: 25 to 50 mg/kg divided into 4 doses 2
- For streptococcal pharyngitis and skin infections: Total daily dose may be divided and administered every 12 hours 2
Special Considerations:
- Otitis media: 75 to 100 mg/kg/day in 4 divided doses 2
- β-hemolytic streptococcal infections: Treatment should continue for at least 10 days 2
- Recent research: BID dosing of 22-45 mg/kg (for MIC 1-2 mg/L) or 80 mg/kg (for MIC 4 mg/L) may be effective for MSSA infections 4
Duration of Therapy
- Skin and soft tissue infections: 7 days, depending on clinical response 1
- Urinary tract infections: 7-14 days for cystitis 2
- Streptococcal infections: Minimum of 10 days 2
Administration Guidelines
- Cephalexin can be administered without regard to meals, as it is absorbed in the upper intestine rather than the stomach 5
- For oral suspension:
- Prepare at time of dispensing
- Store in refrigerator after mixing
- May be kept for 14 days without significant loss of potency 2
Special Populations
Renal Impairment:
- Patients with creatinine clearance less than 30 ml/min require a reduction in dosage proportional to the reduced renal function 5
- Dosage adjustment can be based on creatinine clearance or serum creatinine levels 5
Clinical Considerations
- Cephalexin is effective against staphylococci and streptococci but misses Pasteurella multocida and anaerobes 1
- For patients allergic to penicillins, cephalexin may be an option, except for those with immediate hypersensitivity reactions 1
- Cephalexin does not penetrate into host tissue cells, which likely accounts for its low incidence of side effects 5
Common Pitfalls and Caveats
- Cephalexin is not effective against methicillin-resistant Staphylococcus aureus (MRSA) 1
- For infections caused by MRSA, alternative agents such as vancomycin, linezolid, clindamycin, or trimethoprim-sulfamethoxazole should be considered 1
- Cephalexin may not be effective against Eikenella corrodens in human bite infections 1
- Children may need higher doses per kilogram than adults due to greater body water turnover 5
- Twice-daily dosing regimens, while more convenient and potentially improving adherence, should be used only for specific indications where evidence supports this approach 4, 3